Sometimes, drivers have no choice about taking a detour. An accident on the street, fallen rocks in the mountains, a washed out the road, or construction often means that the police or traffic authority will set up an official detour that drivers should follow to avoid the obstruction. In this case, the route is normally well marked with arrows and signs instructing drivers about what to do. A worker may also stand at the side of the road to give verbal instructions to any drivers who come along. Sometimes, these detours are quite short, but they can also take drivers far out of their way.